Long-term Deflection And Countermeasures Of Long-span Prestressed Concrete Girder Bridge

With the constantly development of science technology and traffic enterprise，long span prestressed concrete girder bridge was widely used, because it has thefollowing advantages that it construct easily,has strong spanning ability and durability.However most of these bridges appeared downwarping problems gradually inoperation stage, It produced negative effects on the bridge’s use and safe. Accordingto this kind of problem, bridge researchers both at home and abroad research focuseson reasons, influencing factors and treatment measures, to bridge with cracks of thelong-term deflection prediction evaluation is still in the exploratory stage.The girder downwarping mostly associated with the beam body cracking,cracking of the beam body accelerated the downwarping of middle unit, bothinfluence each other. The overall stiffness decreases after the beam body cracking, thestructure downwarping will increase In the same size of long-term load resistance.The author analyzed the downwarping’s changes under different fracture height inthis article.The author from the perspective of the law of crack distribution about thelong-span prestressed concrete box girder, establishing crack characteristic parameters,using section analysis method, considering the material nonlinear constitutiverelationship, deducing the equation about fracture height and section stiffness, puttingforward the correction formula about the effective stiffness of pre-stressed concretebeam crack, figuring out the cross-section stiffness reduction factor of differentfracture height.The author modified the model according to the correction coefficient,calculated the corresponding deflection, compared sensitivity of downwarping aboutweb and floor cracks. Also the author analysed the impact on stress and downwarpingwhen the thickness of the web and prestressing force changed, and putted forward themain measures to control long-term downwarping.Through the concrete instance of the real bridge structure analysis, the resultsshow that the fracture height extension of long-term deflection has certain influence,and puts forward the main measures to control long-term deflection of long-span PCbeam bridge for the future long-term deflection prediction evaluation provides thereference.